In December the dam went to the amber alert level, and on Monday council's water testing teams advised that level needed to be raised.

Council routinely monitors the water in all its main dams, with water tests performed by external laboratories and assessed against drinking water and recreation guidelines.

The high level of blue-green algae is about a number of factors that can include higher water temperatures, ratios of nutrient levels in the water, and low flows of water-run-off into the dam.

Gosling Creek is not the only dam affected in the region: Bathurst’s Ben Chifley Dam has now reached the red level.

"We’re at the mercy of the weather. It’s a problem that can’t be fixed until there’s rain," council spokesman Allan Reeder said.

Council advised Lake Canobolas, Suma Park and Spring Creek dams were all rated as green and do not pose a threat to recreational or domestic use.